Enameled winding wires consist of a copper (Cu) conductor and a polymer coating. In the enameled winding wire industry, there has been ongoing research into high durability/high insulation coating film materials capable of securing high insulation even at a high current while increasing coating adhesiveness with copper for processing, flexibility and abrasion resistance. In addition, as the output of a motor/alternator is increased, enameled winding wires are required to have high thermal resistance, such that they are able to withstand high temperature without damage. In accordance with the recent trend toward increased output and decreased weight of the motor/alternator, research has been undertaken into a technology of enameled winding wires capable of having increased and improved functionality.
Polyester or polyester-imide, which have lower thermal resistance but have higher coating adhesiveness and flexibility, is primarily used as a primary coating layer for adhesiveness with the copper conductor, and polyamide-imide, which has higher insulation and higher thermal resistance, is coated as a secondary coating layer. Depending on the requirements for components used in particular application fields, tertiary coatings may be additionally included to increase abrasion resistance or chemical resistance or to provide a low friction characteristic. Breakdown voltage, which is an important characteristic, improves as thickness is increased. However, since the thickness of the coating film is increased as coating is performed in a multilayer structure, an amount of wires wound around a slot of limited coils is reduced. The amount is expressed by a space factor (%), and as the space factor is increased, it is possible to achieve higher density of a current, thereby allowing for miniaturization and higher power of the motor/alternator. There is continuous increased demand for smaller size and higher power of the motor/alternator. Furthermore, when the thickness of the coating film is increased, manufacturing processes increase in complexity, which also increases the cost.
In particular, it is important for a drive motor for an environmental vehicle to have surge resistance. In order to improve the surge resistance, silicon particles are added to an enameled organic material, thereby improving both the insulation and the surge resistance. However, the addition of inorganic materials to the organic materials reduces the dispersibility of the inorganic materials, and a close contacting property between the enameled coating film and the copper conductor are deteriorated, along with the flexibility, such that coating film breakage may occur when the winding wires are processed. To solve these problems, a primary coating for improving the coating adhesiveness, a secondary coating including inorganic materials, and tertiary coating may be incorporated. In addition, a thickness of coating can be thickened to increase breakdown voltage.
As an example, Korean Registration Patent No. 10-1104390 discloses a coating film in which silicas having shapes of spherical, plate-shaped, etc., are added in polyamide-imide (PAI) and dispersed, and coated on copper, wherein when the silica is added in a content of 12.5 wt %, the breakdown voltage is merely increased by about 20% as compared to a case when a silica content is 0 wt %. In addition, a thickness of the coating film is the maximum of 53 μm, which is significantly thick. It is not possible to increase the breakdown voltage while simultaneously reducing the thickness of the coating film. When the silica content is further increased, the breakdown voltage is rather decreased. The reason is that even though the spherical and plate-shaped ceramic have a nanometer size, there is a limitation in increasing a surface area, such that it is difficult to secure binding force with organic materials. When the thickness of the coating film is increased or an added content of silica is increased in order to increase an insulation effect, it is difficult to control the viscosity of the organic materials, and the production cost may be significantly increased. Even though the added content of silica is increased, an agglomeration phenomenon among ceramics is intensified, and binding force in the organic materials is reduced, which may cause a reduction in the breakdown voltage.
Therefore, there has been ongoing research into the development of a coating material capable of securing improved breakdown voltage performance while simultaneously having a thin coating film at the time of manufacturing enameled winding wires used in the motor and the alternator.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.